1. Field of the Invention
This invention relates to an improved process for producing a branched polycarbonate or poly(ester-carbonate) having an excellent blow moldability and vacuum moldability, and more particularly to an improved process for producing said polycarbonate or poly(ester-carbonate) by using a new crosslinking agent.
2. Description of the Prior Art
Polycarbonates are known as resins of high heat resistance, but upon blow molding or vacuum molding, drawing-down of the polycarbonates is apt to occur by their own weight when melted because polycarbonates have a linear structure, and therefore it is difficult to mold an article having a uniform wall thickness and an article of large size.
For the purpose of overcoming the above mentioned drawbacks, there have been proposed some methods of producing branched polycarbonates or poly(ester-carbonate) in the presence of a crosslinking agent.
For example, U.S. Pat. No. 3,094,508 discloses that a part of bisphenol which is a starting material for a polycarbonate is replaced by a trisphenol, i.e. 2,4-bis(4-hydroxyphenylalkylidene) phenol to produce a branched polycarbonate. According to this method, the reaction should be carried out at a limited temperature range of 28.degree.-34.degree. C taking care not to cause the gelation, that is, formation of insoluble and infusible products.
U.S. Pat. Nos. 3,525,712 and 3,635,895 disclose that a thermoplastic randomly branched polycarbonate composition is produced by reacting a bisphenol and a carbonate precursor and the reaction is carried out in the presence of a finely divided solid polyfunctional organic compound. In this process, the crosslinking agent should be added before blowing phosgene, as a carbonate precursor, into the reaction system and further the blowing speed of the phosgene should be controlled.
U.S. Pat. No. 3,541,049 discloses a process for producing branched polycarbonates by using cyanuric chloride.